Respiratory airflow is influenced importantly by active and passive valving mechanisms in the extrathoracic airways. During inspiration, these airways tend to collapse passively, and airway patency is maintained by the action of oropharyngeal muscles. Expiratory flow is also regulated in the upper airways, particularly by the larynx. This project is a continuing exploration of the influence of the upper airways on the control of breathing. Specific plans for the period for which support is requested include (1) studies of the influence of opiate drugs, of CO2 at narcotic levels and of aminophylline on the motor discharge of the hypoglossal nerve and of the abductor and adductor branches of the recurrent laryngeal nerve in decerebrate cats, (2) parallel studies of electromyographic activities of the posterior cricoarytenoid and genioglossus muscles in awake cats, (3) assessment of the influence of hypercapnia and hypoxia on the separate motor activities of the abductor and adductor branches of the recurrent laryngeal nerve, (4) evaluation of the importance of volume-related feedback in regulating the timing and intensity of respiratory motor discharge to the tongue and larynx in cats and human subjects, and (5) an exploration of the control of expiratory abdominal muscle activity in cats. The results of these studies may lead to better understanding of clinical problems of upper airway function, including obstructive apnea during sleep in both adults and infants.